Field of the Invention
The present invention relates to a method for producing a composite piezoelectric body, a method for producing an ultrasound probe, a composite piezoelectric body, an ultrasound probe and an ultrasound diagnostic imaging apparatus.
Description of Related Art
Ultrasound generally means sound wave of 16000 Hz or more, and is applied to various fields such as a defect test and a disease diagnosis because it can examine an inside of an object nondestructively, harmlessly, and in approximately real time. As one of them, there is an ultrasound diagnostic imaging apparatus which scans an inside of a test object with ultrasound, and images an internal state of the test object on the basis of a received signal generated from reflective wave of ultrasound propagating from the inside of the test object. This ultrasound diagnostic imaging apparatus is, as for medical use, more compact and more inexpensive than other medical imaging apparatuses, and has various characteristics, for example, high level of safety because of being free from the risk of exposure to radiation such as X-ray. For this reason, the ultrasound diagnostic imaging apparatus is widely used for a circulatory system (for example, coronary arteries of a heart, etc.), digestive system (for example, a stomach and intestines, etc.), internal medicine (for example, a liver, pancreatic, spleen, etc.), urinary system (for example, a kidney, bladder, etc.), obstetric and gynecologic system, and so on.
In the ultrasound diagnostic imaging apparatus, an ultrasound probe for transmitting/receiving ultrasound to/from a test object is used. The ultrasound probe is equipped with a plurality of ultrasound transducers each of which mechanically vibrates on the basis of a transmitting electronic signal to generate ultrasound, by utilizing piezoelectric phenomenon, and receives reflective wave of ultrasound generated due to an acoustic impedance difference in the test object to generate a received electronic signal. The ultrasound probe is constituted by arranging the ultrasound transducers, for example, in one-dimensional array state or two-dimensional array state.
Heretofore, as such piezoelectric element, a single ceramic material such as lead zirconate titanate (PZT) has been adopted. However, in recent years, a composite piezoelectric body in which ceramic materials are placed at regular intervals and polymer such as epoxy resin fills therebetween has come to be used.
In the case of using such composite piezoelectric body as an ultrasound transducer, it is necessary to form an electrode on the surface thereof. However, there is a problem that unevenness occurs on the surface due to the difference of properties of the polymer and the ceramic material in grinding or polishing processing executed in production process, and as a result, the electrode cannot be formed uniformly. Moreover, if the portion of the ceramic material is dented from the surface of the composite piezoelectric body, namely, if the polymer bulges from the surface of the composite piezoelectric body, the polymer is not restrained on its sides, and thereby sometimes thermally expands freely. Even when such expansion is small, the polymer easily expands/contracts due to heat generated in electrode formation by sputtering, vapor deposition, or soldering. Furthermore, when the composite piezoelectric body is adhered to other components, additional pressure is added thereto in order to remove extra adhesive agent. At that time, stress is concentrated in the polymer, and the polymer, which is softer than the ceramic, is pushed inward. Accordingly, the electrode existing in the vicinity of the boundary between the ceramic material and the polymer is damaged, and sometimes disconnecting of the electrode occurs.
In view of such problems, there is disclosed a technique that performs etching to the polymer portion so that it is dented from the ceramic material portion by utilizing the difference between decomposition rates of the ceramic material and the polymer by plasma etching, and suppresses thermal expansion of the polymer by utilizing adhesiveness in boundary portion of sides of the ceramic material and the polymer, for example, in Japanese Patent No. 4609902.